BATTERY NOTES                                                                                 
R. Kwas Mar 2010, updates - on going.

Charging and Discharging a Lead-Acid Cell
Overnight Battery Discharge
Example of a Parasitic Load
High Parasitic Load from an Audio Amp
Jumping Batteries
Notes on Battery Charging
Battery Tenders Notes
Limiting Available Energy

Critical Battery Parameters

Battery Size

Electron Current vs. Conventional Current
Supporting Information:  Charging System and Battery


Standby or Phantom Current


[This is a compilation of multiple writings, so there may be some repeats of information.]

The Lead-Acid Battery (really a stack of 3 or 6 Lead-Acid Cells, to give the 6 or 12V we need) of your vintage Volvo is a simple, inexpensive, chemical storage device intended to retain the electrical energy needed to power your electric Starter.  There is plenty of generic information out there.  Here are my notes on the subject, including some vintage Volvo specific information: 

History and General Notes:  (Way)-early on, engines had to be hand-cranked to get them going...making driving a car (or at least starting one), a man's job...after a while, they figured: "...let's put an Electrical Starting Motor in there" let women (and girly men) also Start and drive power this beefy electrical motor, and to allow it to develop the significant torque needed to turn over the internal combustion motor, until it self-sustained, a beefy power source was inexpensive, compact, powerful, and rechargeable Lead-Acid Battery was, and to this day continues to be, the answer. 

Lead acid car Batteries in typical service...

To review, the function of a modern car Battery is most importantly, to provide Starting power for the internal combustion motor.  As a secondary function, it will also provide a warm glow to Alice Poobats as you listen to Paradise by the Dashboard Light, while parked, and watching late-night planes come in at the local airport, or while attending nighttime submarine races at the beach.  Once the internal combustion engine is running and self-sustaining, the Charging System is supposed to provide for all of the electrical loads of the after Starting, and being recharged back to full charge, the Battery is really just along for the ride and on stand-by. 

If at some point the Charging System can't keep up with demand (like when the Fanbelt slips, or quad Oscar lights or a 1000W stereo or amateur radio transmitter are turned ON), the battery will  be there to add its power to vehicle power buss to keep the voltage up and things working...for a limited time!  It should be noted that the mechanism by which this switchover takes place is automatic and determined by the voltage levels of both Battery and Charging System output.  It is more of a load sharing arrangement than a hard switchover. 

In the Battery, voltage is determined by chemistry and State of Charge.  In the Charging System, voltage is determined by a reference in the Voltage Regulator and RPMs.  When the two are connected together, the one with the higher voltage provides most of the operating power...and this should normally be the Charging System. do you really know?...not necessarily from a Voltmeter.  You get better information from an Amp meter! (Link to discussion:  Electrical Ramblings, including, Voltmeter vs Amp Meter

Charging and Discharging a Lead-Acid Cell:

Charging and Discharging in a Lead-Acid Cell, explained without too much chemistry. 
REFERENCE INFORMATION:  Electron Current vs. Conventional Current.


Battery Issues:

Overnight Discharge:  Lead-Acid storage batteries are marvelous things.  Although mighty heavy, and filled with highly reactive sulfuric acid (which chemically chews up many things it comes in contact with, including your favorite The Who Maximum R&B oil changing T-shirt), they are an effective, inexpensive way to chemically store electrical energy for a long time…and this is just what is called for in a motor vehicle.  Once the engine (and its electrical generating system) are turned OFF, we must retain sufficient electrical energy to restart it again sometime later…like weeks!  But if your car battery discharges unacceptably quickly, like overnight, you must first determine if this is caused by an excessive parasitic load external to the battery (i.e. headlights left ON), which is not its fault, but a driver error, or some other fault of the Electrical System of the vehicle OR a problem internal to the battery (i.e. a shorted cell, due to an old battery with sulfated plates, which are its own fault).  The simplest way to do this is by process of elimination...I prefer to call this:  Divide and Conquer…

If a battery seems to go dead in only a few hours, like overnight, one of two conditions exist.  Either a constant load in the vehicle is discharging a faulty or forgotten trunk light etc. (discharge by External Load), or the battery has an internal problem causing increased self-discharge (internal).  The best way to determine which is the case is to start with a well charged battery (because a partially charged battery will be easily discharged anyway and would give similar symptoms), disconnect one cable and see if the same discharged condition occurs while disconnected from the vehicle system.  After the test period, reconnect and try starting (better yet, also monitor the terminal voltage while under Starting load this is really a Practical Load Test).  If a discharge due to the vehicle elec system is confirmed, this needs to be located and corrected...a good way is by process of elimination...connect a Multimeter in current mode in series with one Battery wire, and measure the current drawn with everything (supposedly) OFF.  Note that even in this condition, there are some loads which are allowed to and continue to draw a small amount of current i.e. Radio, Clock, memory of a Stereo system.  Anything more that 10mA needs to be checked out (this varies and typically is more with modern equipment) ...and 10mA is plenty for a modern radio which needs to draw a minute amount of power to prevent electronic Alzheimer's.  Pull one fuse at a time to help determine suspect circuit.

High Stand-By Currents (some examples): 

In Volvo 1800s, the clock is an electromechanical unit which will drain a Battery over the long haul.  [Placeholder for actual current measurement.] 


Aftermarket Audio System High Power Amps in Automotive Audio Components are notorious for drawing high Stand-By other words...when OFF!  Measure this to be sure!  I’ve heard of several occurrences where they drew significant current while “OFF”, leading to unexpected rapid discharge of the Battery.  This was initially thought to be a result of a Battery not being able to hold a Charge (...symptoms were similar!  See Link to Brickboard Thread:  ...can't locate it, so below is my best recounting of this thread:  Example of a Parasitic Load).  This is because more than only their control circuit is actually powered and active (apparently, in those cases, drawing significant power!), looking for a control signal from the control head to power up the high power output stage.  This is similar to a typical modern television...the display may be OFF, but the control circuit is powered up all the needs to be...because it is constantly looking for an input signal from the remote control.  Television manufacturers are under pressure to minimize this Stand-By power consumption, but their device is plugged into the wall where lots of power is available, unlike a vehicle, where the power is finite.  

Eliminate parasitic current problems caused by this control circuit with a relay which truly drops power when IGN is OFF.  If presets and memory are  volatile and require power to be ON all the time so as not to experience electronic Alzheimer’s, tell the seller to keep it…buy equipment where memory is non-volatile...better yet, buy equipment which has Stand-By Power consumption specified and an extremely low level (it's possible, more on this below!). 

See:  Related Battery Topic:  Standby or Phantom Current on devices having Soft or Micro-touch Power Switches.

Dealing with Sulfuric battery acid.  In order for batteries to do their electro-chemical magic, they require some pretty strong acid which can quickly oxidize many materials it comes in contact with (including your cotton clothes!).  Wash and neutralize the battery shelf (with baking soda) and the exterior of battery itself with plenty of water before installing.  Because of the damage to the Battery shelf which is common on all vintage Volvos, I further enclose my Batteries in a marine Battery Box.  Route the venting tube of Battery (if present) down and secure with its opening below the frame. Clean the posts and clamps abrasively to shiny metal and install clamps with ACZP (NOT dielectric grease!).  

Battery Maintenance:  A glance at the translucent case to check the electrolyte level whenever one checks the oil should be fine if there have been no indications of electrical problems.  As a rule, Batteries do not require filling often, but if electrical problems have occurred, particularly a high system voltage (due to a Charging System issue) resulting in possible overcharging, which typically "cooks out the electrolyte" at a more rapid rate, level should be checked more frequently...and Battery posts and top should be carefully cleaned as droplets of acid will often collect around the vents under this condition.  If it is an opaque case type, pop the vent caps and look inside...  I don't buy sealed "Maintenance-Free" Batteries...I call those:  "unmaintainable"!  Filling the cells with anything but distilled or Reverse Osmosis DeIonized or (RODI) water, will surely shorten battery life.  Chemical reactions are funny like that...

Load Test:  This is an impressive term simply referring to how well (and how long!), the Battery voltage holds up under a high load (like your Starter might put on it in the winter!).  This gives an indication of how well the Battery can store and give back its energy.  Well equipped garages may have a test box with a high load (a low ohmic value/high power resistance) combined with a Voltmeter with which to perform this...  If your Battery is older than 5years and cranking speed goes down noticeably from at first to after 5 or 10 seconds, its time for a Load test, and maybe a new Battery! 


[This info is somewhat doubled up, but I'll leave it here until the next revision of the article] 


Battery Issues:


Charge/Wait/Check Method:  Start with a fully charged battery.  Disconnect battery - assure a fully charged state with a hydrometer which measures the specific gravity of the acid – a voltmeter only is not really suited for this (LINK:  Voltmeter vs. Amp Meter), or charge it overnight with a line powered charger which is capable of putting out plenty of current [>10A] Note:  The oe Generator based charging system of your 122 is not particularly effective if the battery is completely discharged...i.e. it would take a long drive to fully recharge the Battery!), then leaving it disconnected for a day or overnight.  Reconnect it just before the next starting attempt.  In this manner everything external to the battery has been eliminated from suspicion.  If the battery remains fully charged and capable of turning the engine over just fine, parasitic discharge problem is likely external to battery (like maybe on that Fuse 4 battery powered circuit on a 122). 


If on the other hand, battery is weak or discharged after a day or just 12 hours, when nothing at all was connected, one can be quite certain that it achieved this state all by itself and an internal problem exists within the battery.  Internal problems are quite possible and not as uncommon as one might think.  A replacement is in order!


Measure Parasitic  Current:  If you don’t have the luxury of being able to wait overnight, and you must narrow in a parasitic load external to the battery immediately, or an external parasitic load has previously been confirmed, disconnect the positive battery cable and connect a multimeter, set to measure Current, in series.  With all loads OFF and only normal battery powered loads functioning the absolute maximum current one should see would be about 50mA.  These low level loads include clock, station presets and memory of a stereo, alarm systems etc. (See:  High Stand-By Current, below).  A battery with a full charge can supply these miniscule loads easily and without breaking a sweat for a week.  More than about 50mA will start to become a significant load and this should be located and eliminated...start by pulling Fuse 4 in the 122, or the Battery Power Fuse in the 1800, and observing what the Battery (Stand-By) current drops to. 


The Divide and Conquer rule suggests that this problem should be attributed to either Battery, or the Vehicle.


Battery Problem

Will it hold a charge?  When a Battery's ability to perform is doubted, one of the first things checked is its ability to hold a charge.  It should be fully charged* and a load test should be performed.  The load test can be performed with fancy instruments, but it can also simply be an in-situ starting try.  Only after Battery is checked and proven to be healthy and able to hold a charge, does one need to start troubleshooting the host vehicle!


*  Preferably, charge a completely or partially discharged Battery with a line powered charger overnight.  Disconnect it from the vehicle loads (by disconnecting at least one cable) to remove vehicle from the list of possible contributing unknowns.  Also check electrolyte level to assure plates are completely covered…translucent cases make this possible without removing cell caps.  Sealed batteries which are sold as "maintenance free" are in my opinion also non-maintainable…I don't buy those!     


How old is the battery?  Batteries do slowly loose their ability to hold charge as they age…and even relatively new batteries do have internal failure modes and mechanisms which can lead to their inability to perform.  It's not uncommon to get in excess of 5 years on batteries installed by the factory, but that is typically about the usable life for a replacement battery (the 60 month guarantee has been carefully specified!).


Was battery truly fully charged the night before?  Modern charging systems are quite powerful, having lots of current output capability beyond supplying just the operating loads of a running host vehicle, with which they can relatively quickly recharge the on-board battery at modest around-town RPMs.  Vintage Volvo Charging Systems on the other hand, with their Generators (if they haven't been upgraded yet, LINK), didn't have nearly the extra output beyond running the vehicle, to also put lots of recharge energy back into a discharged battery…especially at low or stop-and-go driving.  Just because the P1800 was driven around the block doesn't by a long shot mean battery is fully charged (that's where the advice, to take an extended highway drive if you need to recharge, comes from)! 


Vehicle Problem

General:  Are all connections having to do with starting clean and tight?  Starting is the highest current load a vehicle battery is subjected to.  All other electrical functions which draw a fraction of that level of current, might work just fine with a marginal connection, but because of the magnitude of current the starter draws, the voltage drop occurring across any less-than-perfect-connection will also be the biggest, and when this voltage is subtracted from the battery voltage, and what's left applied to the Starter, it just may not be enough for the Starter to effectively function.  Battery, Solenoid, Starter and Chassis connections carrying starting current should always be clean and tight!  ACZP (my second favorite product, LINK:  ) helps a lot, especially on battery clamps, given the highly corrosive acids a car battery cannot do without, but which inevitably find their way to the terminals on the outside! 

Also, depending on where in the circuit it occurs, a poor connection can not only give problems starting, but it can also result in degraded charging…so the Battery is not even in a fully charged state when making a starting attempt...a double-whamy!  


6V Vehicles.  Having clean and tight connections is even more important on vehicles with 6V electrical systems, where the system voltage is low to begin with, so we certainly can't stand loosing any little bit (like tenths of Volts!) across poor connections.  Combined with the currents which are typically double those of 12V systems, the resulting voltage drops occurring across poor connections are also doubled...a triple-whamy!   


Parasitic Load Current:  When Ignition Switch is turned OFF, we expect power to be removed from major loads.  Since the Headlights are typically not under control of the Ignition Switch, we need to remember to also turn these OFF when parking…reminder beepers help here! (LINK:  ).  Minor loads like clocks, alarm systems, or audio system presets draw a very small amount of electrical power which any half-healthy battery can easily supply overnight, and for weeks if necessary, so these are allowed to continuously draw their miniscule operating current. 


What one needs to be particularly aware of is battery powered special loads which are "automatic" and which draw a more significant current, but which might remain ON under extraordinary or failure conditions.  Examples of these are glove compartment (OK, at 2Watts, it’s also a pretty minor user) and under hood/trunk lighting (5-10Watts here, so not insignificant, and probably enough to discharge a less-than-fresh battery over a weekend!). 


Occasionally, the charging system itself can develop a problem which results in it drawing current when the Ignition is OFF.  This is where Generator and Alternator based Charging System are quite different.  In an Alternator based System, no special provision is present or required, to separate it from the Battery...the Power diodes of an Alternator are reverse biased when it is not generating output, so do not conduct, and reverse current is blocked.  In a Generator based system, a Cut-Out Contact is necessary to take the Generator Off-Line when it is not putting out (even just at low RPMs!), so that the Armature does not reverse roles and become a electric burden on the Battery.  See detailed description of this here:  Bosch Generator based Ch Sys in Detail.htm#cut-out_contact   


Confirming a Parasitic Load:  When suspecting a continuous parasitic load is discharging the battery, the simplest thing to do is to measure any current flowing while everything is powered down and believed to be OFF.  Disconnect the battery positive cable and place a current meter** in series with (between) battery post and clamp on the cable.  Hard values are difficult to state here, but a measurement in excess of about 10mA is suspect and might be considered an excessive parasitic load current.  As an alternative, a brake light bulb or similar, connected instead of the current-meter will also do in a pinch, but it is only a crude indicator which will obviously not measure the current magnitude.  When using this technique, the bulb should not glow.  Even a slight glow is indicative of a significant parasitic current flowing, and means that a more careful measurement with an accurate meter is called for!  It's best to use an electrical Multimeters...these are inexpensive.


**  Ampmeter of the vehicle (such as are stock on 444 model instrument cluster) typically indicates whole Amps and higher so these are not sensitive enough to indicate a small parasitic load current. 


Locating a Parasitic Load:  When a parasitic current is confirmed by either method, locate the unwanted load, by first removing any Battery Power fuses (Fuse 4 on a 122, Fuse with Brown wires on a 1800), and if this doesn't stop the unwanted current from flowing, continue with this process of elimination by disconnecting further circuits, one at a time, including if necessary, opening more permanent (and unfused) connections like those of the charging system (Generator / Alternator and Voltage Regulator).  It is not possible to give more specific advice here in the absence of specific symptoms, but a good general rule is always to double-check the "last electrical work" which was performed on vehicle!  Once the unwanted load and circuit are located, the remedy is often immediately clear.


Example of a Parasitic Load being related to the "last electrical work" performed on vehicle (based on actual events in a thread, I believe on the Brick board...I couldn't locate the actual thread):  A week after installing a new car stereo, including a monster power amp in the trunk, a dead-battery-in-the-morning-issue occurs on a Monday (when vehicle was not started since the previous Friday)…after the expense of replacing the battery, two weeks later, the dead-battery-in-the-morning-issue occurs again (!)…after days of unsuccessful troubleshooting (and conjecture by well-meaning co-workers during the day at work), the Stand-by current drawn by the power amp (while it is OFF) is finally measured with an accurate Ampmeter (DVM) and found to be on the order of 100mA! 


Explanation:  The "old" battery was indeed getting discharged overnight…but only partially, by the 100mA Parasitic Load, and not to the point of not being able to provide starting power.  Once started, the charging system was able to bring the State of Charge back to an acceptable level and all seemed OK...the vehicle was able to endure this action for a week, but maybe the last trip after starting was a short one which was not able to recover the State of Charge enough, and two days off over the weekend, with that more than negligible discharge occurring, were finally enough to put it over the edge…so symptoms were those of a battery not able to hold a charge, but it was not absolutely confirmed that the battery was the cause…the replacement fresh battery was also able to endure the nightly discharge a bit longer, but in the end, the long-term average was negative, and it too eventually lost to the Parasitic Load which was really the root cause of the dead Battery.  Only when a contactor (relay) was added to control the power into that amp, and truly depower it when it was OFF, was the problem finally and fully resolved. 


Actual Experience with High Parasitic Load from an Audio Amp:  After locating the cause of a dead (new) Battery, Jonathan P. writes:  "...It turns out that the booster I installed to beef up my radio and speaker system never really turns off. Just goes into some dumb standby mode and wipes out the battery in 48 hours. So I installed a relay that resolved the problem.  I basically followed the "last thing I did" advice (see above!) and with my ohm-meter gizmo found I had wired the darn thing into an always on fuse. "  [He didn't measure it, but I just wonder how much current the thing was drawing... when it was doing NOTHING!'s probably a Class A amplifier (known for low distortion) but with high quiescent current.  An its On/Off switch is just a switch on the signal input (clearly not power!), to avoid an On-POP in the speakers.  He didn't give details, but that would be an ideal load for the Ignition Slave could leave the power amp's power switch ON. ]


"Jumping Batteries":  Since we are trying to use a charged battery to "help" another dead or semi-discharged one, both need to be connected in parallel...therefore:  Positive to Positive , Negative to Negative is the rule!  Taking a moment to be ABSOLUTELY SURE of this is important, as getting it wrong can lead to BIG DAMAGE!  

Best Practice for Jumping Batteries: 

Separate Helper Battery to Dead Vehicle:  If Helper Battery is separate and not in a Helper Vehicle, there is little issue, because there is no second Charging System involved! Connect Helper Battery to Dead Vehicle (* See Note 1) and crank away! 

* Note 1.  While connecting, a little sparking may occur when making the last connection and completing the circuit...this is normal and not an indication of a problem, but since we know Batteries produce hydrogen, it's best practice to keep that spark away from any hydrogen concentrations (to prevent your own personal Hindenburg situation...). 

Picture of the probably one of the best known hydrogen explosions!

...not to make a bigger deal of this than necessary, I simply exhale across the top of the Battery when I'm making the last connection (persons which have seen the author do this and were wondering "what the heck is he doing now?", now know!).  [I looked for videos on YT of exploding car Batteries, but was only able to find intentionally set-up situations, as this is a fairly unusual occurrence and actually capturing a truly accidentally occurring one on video is even more rare...]

Helper Vehicle to Dead Vehicle - (The Absolute Safest Way):  If Helper Battery happens to be in a vehicle (which naturally has its own Charging System), it is always good practice to not connect the two Charging Systems together, while they have an output.  This means, connecting the two batteries together with the jumper cables, then letting the Charging System of the running Helper Vehicle put a bit of charge on the dead battery in the Dead Vehicle, for a few minutes, before making any Starting attempt.  Then, to assure the Charging System of the Dead Vehicle does not damage the Helper Vehicle, or the two Charging Systems fight each other (layman's term for tying two high current capable Batteries and Charging Systems together) in that each tries to keep the combined system at a different voltage, the engine (more importantly:  Charging System) of the Helper Vehicle should be STOPPED (before making Starting attempts), while leaving the jumper cables connected in place...then making the Starting attempt on the Dead Vehicle.  In this way, the Helper Battery will still be helping the partially recharged Battery of the Dead Vehicle, but after starting, only one charging system will come on-line, and there is no chance of damage to either vehicle's electrical system.     

Once the Dead Vehicle is Started,  the immediate issue is under control, but we should try to understand and address the root cause...if a Load was left ON to cause the Dead Battery (driver error, see above) then recharging Battery may be enough...if we don't have an explanation for the Discharged condition, we need to monitor vehicle operating conditions to understand why the Dead Battery occurred, lest it occur again.  In any case, it's a good idea to take a little ride and allow Charging System to put a good charge on the Battery.  If the Charging System on our vintage Volvo is still an OE Generator, the ride should certainly be at elevated RPMs so that the Generator is in its' maximum output range.  This is not so much of an issue with a Volvo upgraded to an Alternator, because these put out well even at low RPMs.  (See:  Comparing Generators and Alternators  )  During the ride, we can monitor the Charging Current on our Amp-Meter, to see when Battery is fully charged again. 

Notes on Battery Charging:  
High Rate of Charging:  A Charging rate over 10Amps.  All Charging of the Battery generates Hydrogen, (Chemical Reaction here:   but quick Charging with any charger (including those located in a vehicle...also known as the Generator/Alternator Charging System) generates increased hydrogen.  If this is done in a moving vehicle, there will be plenty of ventilation to dissipate the hydrogen, but if there is a high charging rate like in a parked vehicle, a significant amount of hydrogen may collect in a confined area.  In this case, venting is more important, to prevent the possibility of your own miniature Hindenburg situation!  Open the hood and garage door to allow Hydrogen to vent away!

Medium charging current 2-10Amps.  Overnight chargers.  These work fine and they are gentle on the Battery. 

Slow or Trickle charging...up to 2Amps.  Good for replacing the charge lost through self-discharge, and keeping a Battery of a stored vehicle charged to max.   

Battery Tenders Notes: 

My response to a Swedespeed Thread where a Battery Tender was getting "pretty hot".:. [posting 170, 171 in this long thread] 

"(A) Battery Tender is not a Bat Charger! is intended to replace the minimal self-discharge of a Bat during storage only, and its' wallwort is likely rated for under 1 A...if you hook it to a discharged Bat, the Bat will draw a lot more than that trying to attain full charge (to the current limiting point of the BT), so you are doing that BT no favors, and I would be little surprised if in a future posting you tell us that your Bat destroyed your BT...I recommend against it!  Charge Bat either with properly functioning vehicle Chg Sys or a line powered charger, and use the BT for its intended purpose only... "


Limiting Available Energy, during Electrical Check-out: 

The Battery stores and can provide lots of electrical energy! has to...certainly when Starting!...but this is a lot more than you might want in certain the initial check-out of major changes/repairs to an Electrical System!  Below is an excerpt from an e-mail thread with an owner who was powering up his vehicle system for the first time after having having just completed major electrical work...namely installing a new harness, or in his case, converting his P1800 Electrical System from those (3!) horrid Lucas Fuse Blocks (See: , to a 9 fuse holder from a 140 (See:  ...I consider this a sensible upgrade if you don't mind the non-factory appearance, and I'll take good reliability and multiple fused circuits in a P1800 any day over the original questionable design and execution!  This change can also be considered a major electrical surgery on the system, so Limiting the Available Energy during initial check-out is a very good idea!

Limiting maximum available electrical energy:  To limit available electrical energy, simply connect a temporary fuseholder in series with Battery Positive Terminal.  Into this fuseholder, install a fuse of modest current more than 10 or 20A.  This will allow all electrical functions to be operated normally during check-out, except Starting and Charging.  If errors have been made during electrical work, which result in short circuits on the power wiring, or even just drawing more than the fuse rating, fuse will blow immediately (saving harness and possibly more precious wiring or components), and making the area one should concentrate troubleshooting on clear if not obvious.  Replace fuse and complete checkout until ALL functions work as expected.  Only once all functions have been found to be working as expected when their respective control is activated, [and none are found to be working unexpectedly, or other anomalies are observed!] the temporary fuseholder can be removed, and Battery Clamp can be connected to Post normally to allow Starting. 

Function of Charging System, which is off-line while engine is not running, must be checked after Starting.  Troubleshooting of a non-working Chg Sys (indicated by a system Voltage which does not get pulled up when Chg Sys comes on-line) is handled in detail elsewhere on the SW-EM site, but assuring cables and connections of the Chg Sys are in place and snug, exhibiting nothing unusual is always a good start.  

From Correspondence: 

Sent: 16 July 2007 12:01
To: Russell T
Subject: Re: Rear interior lights 1967 Volvo 1800


If you are not totally confident and want to add an extra measure of safety for the initial power up checkout, I suggest putting a 20A fuse in series with Battery for the initial power up...this will allow you to check function of all items except starting...if no anomalies are found, connect directly, with no current limiting, and proceed...R


----- Original Message -----

From: Russell T.

To: 'Ron Kwas'

Sent: Monday, July 16, 2007 6:46 AM

Subject: RE: Rear interior lights 1967 Volvo 1800



Like you I took notes and identified the circuits, so hopefully this may help people who envisage this conversion in the future.

Before I take pics or release my notes I want to power up the system…………!

As always thanks for getting back quickly

Best regards



From: Ron Kwas
Sent: 16 July 2007 11:41
To: Russell T.
Subject: Re: Rear interior lights 1967 Volvo 1800




Correct assessment!  This is a cutesy design that few are aware of...especially if you don't have an owners manual...careful review of the wiring diagram would give a hint though as I recall...[See also:  Local Control of the Courtesy Light  ] 

All in all how did the conversion any pix?


Regards, R


----- Original Message -----

From: Russell T.

To:  '*************************'

Sent: Monday, July 16, 2007 2:49 AM

Subject: Rear interior lights 1967 Volvo 1800



Finished wiring in the 140 fuse box this weekend, happy with the final result and it looks a lot neater. I also isolated the overdrive circuit onto its own fuse way.

Whilst tracing the various circuits I had what I thought a full earth on the interior lights. Tracing the circuit identified it to the rear lights and looking at the construction/operation it appears when the light ‘glass’ is pulled out to turn the light on it releases two spring contacts which earth to the housing of the light.

It appears my ‘full earth’ was in fact the lamp activated and a normal part of the system operation. Am I correct or is this a problem?

Thanks in advance




From my posting in response to:  What battery for 121 Amazon?

Critical Battery Parameters:

Nominal Voltage of System (...could be 6V or 12V for your 121, check Owners Manual or by counting number of cells/caps on cells of Bat. 3 for 6V, 6 for 12V)

Amp Hr Rating (Product of Current and Time...or Bat Reserve can push or pull this a bit from the original 60AH specified (for 12V)...depending on operating conditions...for instance, if you are Auto-Crossing and you have removed your passenger seat, spare tire, carpet, dieted, and taken all the change from your pocket to save weight, and low weight is your absolute goal, you could install a tiny, lightweight motorcycle Battery, and Start on a Helper Battery (which gets left in the pits), and go racing...but if you are driving to the Nordkap to visit your uncle Olaf in January, you might want to fit the biggest Battery you can physically fit on the shelf in order to have lots of Reserve Starting power...just in case!)

Physical Size (Bat shelf is generous on an Amazon so will fit just about any reasonable size.)

Terminal Type and Locations (Pos and Neg Wires will typically have compression clamps, so the Bat must have the corresponding posts, and Pos and Neg wires are sized so that they will need these posts located on the correct side of the centerline of Bat....otherwise wires will need to be adjusted in length/location.)


Battery Size:  The battery shelves on vintage Volvos are quite generous and will accommodate a huge battery necessary for starting your vehicle in winter while above the arctic circle, plus lots of more moderate climates, a "Series 24" size (See Reference Info, Battery Size ) with normal posts located as shown below should cover your year-round needs...and if you're ultra weight-conscious, and have removed the passenger and back seats of your auto-crosser Amazon, as well as all the change from your pocket, a motorcycle battery relocated to where the passenger seat used to be (to tuck in its' mass and minimize polar inertia!  See Link:  ) would do it too...and maybe you should say no to that second baconburger...

A super clean 123GT engine compartment showing Battery location, including terminals
(note terminals are off-center on Battery).  



Battery Size:

Electron Current vs. Conventional Current.  It's just semantics, and convention, and engineers have been aware of it for a long time...sort of like saying water pours down, out of a bucket, and air flows up, back into the long as we decide up-front which one we're going to talk about and keep it consistent, what's the difference!  [The author uses the convention of Electron Current Flow in all discussions where it matters. ]

Supporting Information:  Charging System and Battery  General explanation of Alternator Charging System function, and the important functions the Battery provides  (part of Tech Article:  123GT Reliability Weakness and Simple Improvement ).



Brickboard Thread:

Everything you always wanted to know about Lead Acid car batteries.  Bill Darden has compiled a very good compendium of info:  CAR AND DEEP CYCLE BATTERY FAQ 2015 by:  Bill Darden (no relation to the author other than finding his good info through a search)

When was Battery manufactured?  Batteries have a limited operational life, while OEM Vehicle manufacturer's Batteries can often easily last more than 5 years... that is about the limit for aftermarket Batteries on the other hand, so in the course of troubleshooting possibly Battery related electrical issues, it's nice to know when a Battery was manufactured.  All manufacturer's have their own coded is the Secret Decoder Ring to manufacturer's markings to determine battery age (Listed under:  7.6.  Freshness)  This outfit sells a small inexpensive charger, specifically intended to replace the energy (charge) lost to self-discharge while a battery is in storage and not in use.  Although they incorrectly state that oxygen is flammable (oxygen itself IS NOT just allows anything burning - the Fuel(!) - to burn faster and more intensely!...picky, picky, picky ...remember the Apollo 1 Oxygen Fire), they have compiled a lot of good, usable Battery related info, mainly in support of their product.  I have not evaluated their product for quality of engineering and reliability, I therefore do not specifically endorse it, but it does look to me like they have done their homework, considering all of the engineering and use questions, and it is a fact that connecting a maintenance charger to a battery is good in the long-term as it keeps the battery fully charged and this is the preferred condition of a lead-acid battery!  Any readers with first-hand experience with this product are invited to relate this to the author.  



Standby or Phantom Current on devices having soft or microtouch power switches.  This is a related Battery Topic, not specifically about automotive Batteries...but battery powered handheld devices, and it seemed this was the best place to get it off my chest! 

Soft Touch Power Switches and Wasted Battery Energy -  Devices with soft touch ON/OFF switches will typically will typically draw a "small amount of Battery power" while they are waiting for you to push that cute, soft, little, designer ON /OFF button...trouble is, a "small amount of Battery power" adds up! ...if you have one of these devices and don’t use it for an extended time, and you didn't follow the small print in the instructions to "Remove batteries when not in use", you can be just about guaranteed to have to replace its Batteries before the next time you use it, even if the device was parked with good Batteries (this to me is infuriating!)...because for that entire month or three, while sitting there waiting for you, and supposedly OFF, the control circuit was actually powered (minusculy, but nonetheless powered, and drawing that "small amount of battery power" the entire time!) and waiting with baited breath, for you to push that piss-whimpy ON/OFF button! 

This just another example of wastefulness and also woosification of America in my opinion!  These switches should be labeled Stand-by, not ON/OFF!

Give me a real switch any day...which goes CLICK with authority, which truly removes (ALL) power when in the OFF position, instead of designing equipment with this soft touch crap which needlessly wastes batteries before their time...then marching on Earth-Day!  

Recommendation:  As it directs in the manual:  Remove batteries when not in use...from these devices ...of course this is a nuisance as it is a bit of a procedure and it separates the components allowing some to get lost...not to mention that the device is now not "Ready for Instant Use". 

As another option, simply place an insulator such as a strip of thin but strong plastic (a colorful and highly visible strip, cut from a candy wrapper will do nicely!) between the terminals of one battery and its neighbor, or one battery and one of its contact clips (in other words, ANYWHERE in series with the battery array), and let this show out the battery door (I cannot take full credit for this simple and groovy idea…inexpensive electronics where “batteries are not sold separately” often come with an insulating strip such as this, which has to be removed before the first use...I guess they just don't know how long their junk will sit in the cargo container crossing the Pacific)...this Phantom Current Killer insulator will break the circuit just like a real power switch and eliminate the Stand-By Current consumption...and the batteries will hold their charge as if they were uninstalled…a quick pull to remove the insulator (which because of its colorfulness, you can't miss, if you’ve forgotten about it!), when you want to use the device, and you’re back under (full) power, "Instantly", having wasted none!  Now that's what I call being a true conservationist (I'm conserving resources and my own money)!

My Petzl Ultrageek-this-is-America-and-I-can-change-the-oil-at-midnight-if-I-feel-like-it headlight, with a soft-touch, multifunction switch, retrofitted with a colorful Phantom Current Killer plastic label from some tasty Polish candies that Wendy got for me, between one Battery and it's clip, and snuck out the side of the battery compartment get the idea!

This seems not to be an issue on Infra-Red remote controls, like for a TV...on these, the Batteries seem to last forever...I expect since the final load in these devices is a flea-powered IR-LED, they can put the LED power right through the soft-buttons, and the rest of the time, when no button is pressed, Battery has true zero draw, even when I am giving them a high-use, Life-Test, scanning for something to watch, other than the Golf-Channel (Golf sucks!) or "Aliens Guy" with the scary hair, and his impeccable logic...

...I expect he drives a French car!


While on the subject of handheld, battery powered devices, see my recommendations on how to keep Low Voltage/Low Current battery connections protected and this equipment operating, ACZP is not the answer!  See:  Deoxit D5 Additional, My Recommendations  


Current consumption and battery drainage during Off/Standby, has been recognized and is addressed by some manufacturers... 

From:  (my Highlights)

My Suggestion to Manufacturers:  Add a miniscule slide-switch (a Real Power Switch!) into the Battery compartment, and relabel the ON/OFF switch Standby, which it is!


Finally...In a pinch, we can often take liberties, but I don't think this is what they mean by the term Battery Clamp:

Image Source:  Stolen from somewhere...note the groovy (intermittent) self-discharge feature...


External material sources are attributed.  Otherwise, this article is Copyright © 2001-2024.  Ronald Kwas.  The term Volvo and Petzl are used for reference only.  I have no affiliation with these companies, other than to try to keep their products working for me and reliably, and to help other owners do the same.   The results and highly opinionated thoughts presented here are from my own experience, and should be used in conjunction with normal, careful shop practice, or can be ridiculed and laughed at, at your discretion.  Exercise extreme caution when working with lead acid storage batteries which use sulfuric acid to store large amounts of electrical energy, and which produce hydrogen!  Remember, you alone are in control of your future, your knuckles, your eyesight, and it is up to you to keep your Battery from doing a miniature (yet equally as impressive) impression of the Hindenburg! 

As always, if you can supply related additional objective info or experience, I’d appreciate hearing it, and will consider working it, along with the odd wise*** comment, into the next revision of this article.  You are welcome to use the information presented here in good health, and for your own noncommercial purposes, but if you reprint or otherwise republish this article, you must give credit to the author or link back to the SwEm site as the source.  If you don’t, you’re just a lazy, scum sucking plagiarist...and the Boston Globe wants you! 

Aliens are real!

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